人疱疹病毒8型复制与SUMO化修饰之间的相互作用及机制研究

SUMO化修饰调节蛋白的活性和定位，控制生理活动及抗病毒反应，是病毒优先攻击的目标之一。病毒复制可改变SUMO化水平。人疱疹病毒8型（HHV-8）编码SUMO引导的泛素连接酶RTA和SUMO连接酶K-bZIP，双向调节SUMO化修饰。我们推测RTA在复制早期激活K-bZIP以提升SUMO化水平，随后降解K-bZIP导致SUMO化水平骤降而开启晚期基因并组装毒粒，凭RTA两度逆转SUMO化水平实现对病毒裂解复制的时序控制。拟利用HHV-8重激活和感染模型，研究：1）病毒复制对宿主SUMO化水平和修饰酶的影响；2）RTA激活和降解K-bZIP对SUMO化修饰的调节；3）病毒不同启动子对K-bZIP抑制和SUMO化水平依赖性的差异。阐明HHV-8复制对宿主SUMO化修饰的影响，揭示宿主SUMO化水平的波动与病毒基因表达时序间的关系，初步建立RTA通过控制宿主SUMO化水平调节病毒复制的时序模型。

Post-translational modification by small ubiquitin-like modifier (SUMO), termed SUMOylation, has emerged as a rapid and dynamic regulator of protein localization, stability and activity. SUMOylation controls a variety of important cellular processes, including signal transduction, replication, chromosome segregation, DNA repair, and is therefore a preferential target for viral attack. Human herpesvirus 8 (HHV-8) seems to have evolved mechanisms that directly or indirectly modulate the SUMO machinery in order to evade host immune surveillance, thus advancing their survival. Interestingly, HHV-8 encodes RTA (replication and transcriptional activator), a SUMO-targeted ubiquitin E3 ligase (STUbL), and K-bZIP (KSHV-encoded basic leucine zipper protein), a SUMO E3 ligase, which functions oppositely. We hypothesize that at the initial stage of viral replication, RTA activates K-bZIP, up-regulates the global SUMOylation level to repress host immune-related genes. However, subsequently, after the accumulation of viral early products, RTA starts to degrade K-bZIP, down-regulates the level of SUMOylation, so that viral late genes can be expressed and virion assembly can be accomplished. It is likely that as the only switch protein to trigger viral reactivation, RTA controls the replication schedule probably through modulating host SUMOylation. To validate this hypothesis, in this proposal, HHV-8 reactivation system and the de novo infection system will be utilized to investigate 1) the effects of HHV-8 replication on the cellular global SUMOylation, and on the level of SUMO-catalyzing enzymes; 2) the mechanism of RTA activation and degradation of K-bZIP and their roles in the modulation of cellular global SUMO levels; 3) the dependence of different viral promoters on the repression of K-bZIP and on the RTA-modulated SUMOylation levels; and 4) the effects of cellular global SUMOylation on the HHV-8 replication. The objective of this proposal is to establish the model that RTA controls the schedule of viral replication via its dynamic regulation of K-bZIP and the cellular SUMOylation level. This study will contribute to the understanding of the interaction between HHV-8 replication and host SUMOylation, and will facilitate the development of new strategies to interrupt viral replication.